Lubricant-coolant emulsion stabilization and reuse



United States Patent 3,408,843 LUBRICANT-COOLANT EMULSION STABILIZATIONAND REUSE Lyle Treat, Ferguson, Mo., assignor to The Dow ChemicalCompany, Midland, Mich., a corporation of Delaware Continuation-in-partof application Ser. No. 443,528, Mar. 29, 1965. This application Oct.26, 1966, Ser. No. 589,730

8 Claims. (CI. 72-42) ABSTRACT OF THE DISCLOSURE A lubricant-coolantoil-in-water emulsion used in the shaping of a metal is stabilized andkept filterable by periodically adding polycarboxylic acid chelatingagent, such as a polyacetic acid, or salt thereof, in the requisiteamount to adjust and maintain the hardness level of the emulsion belowabout 400 ppm. (expressed as CaCO and the pH value in the range of aboutto 11. Preferably the hardness level is maintained in the range of about25 to 400 ppm. and the emulsion is also filtered to remove solidparticles larger than about 0.5 to microns maximum dimension.

The present application is a continuation-in-part of prior applicationSer. No. 443,528, filed Mar. 29, 1965, now abandoned.

The invention relates to the hot or cold working, cutting or othershaping of metal in any operation wherein there is used a flowinglubricant-coolant oil-in-water emulsion which is recycled and reused.The invention also relates to the composition of such emulsions as wellas a method for improving such emulsions.

For the purposes of the following description and the appended claims:(1) aluminum and its alloys containing at least 70 percent by weight ofaluminum are hereinafter referred to as aluminum; (2) magnesium and itsalloys containing at least 70 percent by weight of magnesium arehereinafter referred to as magnesium; (3) copper and its alloyscontaining at least 50 percent by weight of copper are hereinafterreferred to as copper; (4) iron and its alloys containing at least 75percent by weight of iron are hereinafter referred to as ferrous metal;(5) the operations of rolling, working, drawing, cutting, milling,scalping, drilling, or grinding and the like of metals are hereinafterreferred to variously, as method of shaping a metal, metal shaping, andthe like; and (6) the phase flowing lubricant-coolant oil-inwateremulsion is intended to encompass such emulsions which are sprayed onthe workpiece or tool.

In methods of shaping metals in which lubrication is required it hasbecome common to use an oil-in-water emulsion in place of prior usednon-aqueous hydrocarbon lubricants. For example, in rolling a metal suchas aluminum, magnesium, or steel through steel work rolls it is usual touse an oil-in-water emulsion to flood the rolls and the work stock. Theemulsion serves the dual functions of both coolant and lubricant. As acoolant in cutting operations, the emulsion helps to control thetemperature of the cutting tool. As a coolant in other shapingoperations, for example, in rolling, the pattern of dis tribution of theemulsion on the work rolls is regulated to control the temperaturegradient of the rolls transversely to the work stock and hence the shapeof the rolls is controlled. The rate of flow of the emulsion onto themetal being shaped regulates the temperature thereof during the variousstages of shaping.

As a lubricant, the emulsion serves: (1) to control the frictionalforces existing between the workpiece and the Work tool; (2) to promotethe development of desired tool coatings during the shaping process,e.g., roll-coating during rolling; and (3) to prevent excessive transferof metal from the workpiece to the tool or from the tool to theworkpiece, e.g., between the rolls and the workpiece as in rollingoperations. 7

Typical lubricant-coolant oil-in-water emulsions that have been used formetal shaping operations such as rolling or cutting have consistedessentially of from about 0.5 to 20 percent by weight of an oil inwater, the oil being a mixture referred to in the trade as neat solubleoil or soluble oil. Such neat soluble oil is widely sold as aconcentrate containing, generally, about 70-90 percent by weight of abase oil, such as a light mineral oil, from about 1 to 20 percent byweight, based on said neat soluble oil, of one or more anionic and/ornonionic oil-inwater emulsifying agents and the balance substantiallywater. For most metal shaping operations, the neat soluble oil must alsocontain from about 0.5 to 15 percent by weight of lubricity additivessuch as long chain fatty acids and salts or esters thereof, e.g.,alkanolamine soaps, or, esters such as butyl stearates which serve asextreme pressure agents. Such emulsions are made up conventionally byadmixing one of the commercially available substantially water-freeconcentrates with water. The commercial concentrates usually contain upto 0.5 percent by weight of a bactericide and from about 0.5 to 5percent by weight of a coupling agent, i.e., a substance whichstabilizes the concentrate during storage prior to use.

The composition of the neat soluble oil itself forms no part of thepresent invention. The method and composition of the invention areusable with substantially all of the commonly known and usedcommercially available neat soluble oils, without modification of thesoluble oil per se.

Suitable commercial compounded oils, i.e., soluble oils, include, forexample, Solvac 1535G, Prosol 44 and Prosol 66 supplied by Socony MobilOil Company, Rollex A supplied by the Shell Chemical Company, Majestic#101 supplied by Fiske Brothers Refining Com pany, RolKleen #53 suppliedby the D. A. Stuart Oil Company, Ltd., A- supplied by Far Best, W.S.51821 supplied by the Humble Oil Company and Tandemol C86 and TandemolK87 supplied by E. F. Houghton and Company.

A typical neat soluble oil that is commercially available has thefollowing general composition, by weight:

The base oil used in making up a neat soluble oil generally is selectedfrom a light hydrocarbon or light hydrocarbon mixture having a viscosityof about 40 to 200 Saybolt Universal seconds (SUS) at 100 F. However,other lubricious materials such as fatty oils, e.g., palm oil, orsynthetic materials, e.g., palm oil substitutes, are also used as a baseoil in making up soluble oil. Such other lubricious materials may haveviscosities as high as about 850 SUS.

For the purposes of the following description and the appended claims,the term base oil is understood to encompass the light hydrocarbon orhydrocarbon mixtures recognized as light mineral oils, in addition tolubricious materials including vegetable oils, such as palm oil, animalfats, such as lard oil, and palm oil substitutes and the equivalentsthereof, e.g., polyglycols and ethers and esters ample: (1) alkylarylsulfonates such as the higher ankylbenzene sulfonates wherein higheralkyl means an alkyl group having at least 8 carbon atoms, e.g., C H C HSO Na; (2) fatty alkyl sulfates such as CH (CH OSO Na; (3) thesulfonated fatty amines such as C11H33 CON (CH )C H SO Na; (4) thealkali metal salts of sulfonated fatty acids; and the like. The otheralkali metal salts of these compounds and the triethanolamine salts areequivalents of the sodium salts described above. The alkanolamine soapsof long chain fatty acids are particularly suitable e.g., thediisopropanolamine, diethanolamine or monoethanolamine salts of oleicacid, palmetic acid or stearic acid, the salts being useful singly or asmixtures.

Suitable nonionic oil-in-water emulsifiers include the nonionic etherssuch as those derived from alkylphenols and ethylene oxide, e.g.,C8HI7C6H4OC2HQ(OC2H4)XOH wherein x has a value of 9 to 14 or more, theprimary alcohol-ethylene oxide adducts, and the secondaryalcohol-ethylene oxide adducts.

When one of the described oil-in-water emulsions is placed in service inmetal shaping operations it tends to work well initially both as acoolant and as a lubricant,

althoughit is commonly observed that the metal surface obtained in metalshaping operations is improved after several days of using the emulsion.With continued recycling and reusing, the emulsion ordinarilyaccumulates solid particulate matter including metal fines, metal oxideparticles, oxidized oils, soil particles and general air-borneindustrial contamination. In addition, hydraulic oils and bearinglubricants occasionally enter the emulsion as a result of accidentalleakage and are collectively referred to as tramp oil. As a result ofsuch contamination and also as a result of general use of the emulsionthe emulsion begins to break and the droplets of the oil phaseagglomerate into larger droplets some of which coalesce sufficiently toprovide a substantial quantity of continuous free oil phase.

Separation of free oil, i.e., base oil, from the emulsion affects thelubricity properties of the lubricant-coolant in a manner adverse torolling operations leading to refusal of the mill, in rollingoperations, to accept the workpiece being fed into the rolls unless therolls are set for only a small reduction of the workpiece. Thisseriously reduces the percent of reduction that can be achieved perpass. Sometimes the mill will not accept the work piece unless the rollsare set for zero reduction. In cutting or grinding operations, excessivelubricity may reduce the effectiveness of the cutting or grinding tool.The excess continuous free oil phase can also plate out on the workpiece in noncutting shaping operations such as rolling, and lead toharmful staining problems during subsequent processing such as heattreating. Similar harmful effects are observed regardless of whether thecontinuous free oil phase comes from the breakdown of the emulsion orthe accumulation of tramp'oil which is neither emulsified nor removedfrom the system during recycling.

For the purposes of the present invention, an emulsion which contains nomore than about 0.2 percent by weight of continuous free oil phase isconsidered to be free of such free oil phase.

The accumulation of solid particulate matter adversely affects thesuccess of shaping operations such as rolling. The particulate mattertends to become embedded in the metal surface leading to undesirablesurface appearance. Embedded particulate matter interferes with surfacetreatments such as anodizing or coating. In the past the foregoingproblems have necessitated skimming off some of the floating impuritiesfrom the emulsion and/or settling solids as a sludge on the bottom oflarge settling tanks. T his. has not been entirely successful becausethe removal is not nearly thorough enough. skimming is also disad- 4vantageous because some good emulsion is removed with the impurities andas a consequence the addition of makeup soluble oil is necessary. Someoperators have tried filtering the lubricant-coolant emulsion but thishas not been successful for any extended period becauseof blocking ofthe filter. All of the causes of blocking or the filter are notunderstood but it isb'elieved that contributing factors are the tendencyof the continuous free oilphase' to accumulate on the filter media thusblanking off or blocking further passage of both aqueous phaseanddroplet size oil phase through. the filter also, the formation andaccumulation of polyvalent metal soaps in the emulsion. Only filterswhich pass relatively large particles have remained operable for longperiods, and these filters are relatively ineffective. In mostinstances, operators have simply discarded the entire batch ofemulsion/after 3 to 6 weeks or less of steady use. A few systemsemploying a large reservoier of emulsion have operated for somewhatlonger periods. In the case of rolling mills this involves a substantialquantity of emulsion.

Typical industrial emulsion systems vary in size from perhaps 5,000 to10,000 gallons or less for smaller cutting or grinding operations tosystems as large as 100,000 to 500,000 gallons for large rolling mills,some of which require the circulation of 1,000 to 10,000 gallons ofemulsion per minute to one or more mill stands.

It is therefore a principal object of the present invention to providean improved method for shaping metal in which there is employed alubricant-coolant oil-in-water emulsion which is recycled and reused.

Another object of the invention is to provide a method of stabilizingand reusing a lubricant-coolant oil-in-water emulsion in metal shapingoperations.

Another object of the invention is to provide a method of removingparticulate matter and eliminating or reducing continuous free oil phasefrom lubricant-coolant'oilin-water emulsion, apart from a normal levelof about 0.2 percent by weight of such oil phase, which is notdetrimental in effect.

A further object of the invention is to provide a method of increasingthe service life of lubricant-coolant oil-inwater emulsions used in theshaping of metal.

Yet another object of the invention is to provide an improvedlubricant-coolant oil-in-water emulsion for use in metal shapingoperations. I

These and other objects and advantages of the present invention will bemore clearly understood by those skilled in the art upon becomingfamiliar with the following description and the illustrative examples.

It has been discovered that a conventional rolling or cutting oilemulsion is improved by the addition thereto of an alkaline alkali metalor ammonium or'amine salt of a polycarboxylic acid ehelating agent in'anamount sufiicient to chelate calcium, magnesium, aluminum, heavy metalor other polyvalent metal ions present or accumulating in such anemulsionwhereby the hardness content, expressed as CaCO is reduced belowabout 400 p.p.m., and the emulsion pH is brought into the range of about5 to 11. Where foaming is a problem it is much preferred to bring thehardness content to about 25 to 400 p.p.m. In addition to the initialadjustment, the maintenance of a controlled level of hardness contentbelow about 400 ppm, expressed as CaCO and a pH in the range of about 5to about 11 is essential. Such management of the emulsion substantiallyprevents oil separation therefrom and has the following furtherimportant effects: (a) the emulsion is stabilized so that it can befiltered through a mechanical filter capable of removing solidparticulate matter larger than 10 to 20 microns size, and preferably,larger than .1 micron, such as a filter provided with a siliceousprecoating; (b) solid'particulate contam' ination such as dirt, metalfines, and metal oxide particles are readily removed on the filterwithout premature filter blank off problems; (c) light viscosity trampoils leaking into the system are substantially emulsified thusminimizing the quantity of free oil phase; and (d) oxidized oils andreaction products thereof are removed on filtration.

An important aspect of the present invention is the discovery that theparticle diameter of the globules of emulsified oil is at least partly afunction both of pH and hardness content of the emulsion, the nature andconcentration of the emulsifying materials present being alsocontrolling factors. This role of hardness had not been appreciatedheretofore. Both calcium and magnesium hardness are generally derived inpart from the water used to' make up the emulsion. Large quantities ofwater are frequently and periodically added in many metal shapingoperations to replace losses due to evaporation bringing about theaddition of substantial amounts of calcium and magnesium hardness.Calcium, and to some extent magnesium ions, also enter the emulsion fromconcrete mill pits or sumps and storage tanks in which the emulsion isreceived or stored. Especially in the case of magnesium and aluminum,the work piece employed is a substantial source of magnesium and/orcalcium and/or aluminum ions. These appear to be the main sources whichprovide for a build-up of hardness content in the emulsion, particularlycalcium and magnesium, as the emulsion is recycled and reused.

While substantially all of the hardness ions could be chelated with thechelating agents employed in the invention, if desired, foaming of theemulsion during pumping and spraying operations tends to be a problem inmost operations when the hardness level falls too low. Where foamingtends to be excessive and undesired, a hardness level in the range of100 to 200 p.p.m. expressed as CaCO is preferred; where foaming is lessof a problem, a hardness level in the range of 25 to 100 p.p.m. ispreferred.

' The metals which may be rolled or shaped according to the presentinvention include aluminum, copper, ferrous metal, such as steel, andmagnesium. These metals may be shaped cold, or at temperatures as highas about 1050 F., using the emulsion of the invention.

7 The chelating agents used in the method of this invention are thealkali metal or ammonium or amine salts of polycarboxylic acids,including citric acids, tartaric acid, the alkylene amino polyaceticacids, and mixtures of any of the said salts of such polycarboxylicacids. The alkylene amino polyacetic acids includeethylenediaminetetraacetic acid and its well-known homologs and analogssuch as N-hydroxyethylenediaminetriacetic acid,diethylenetriaminepentaacetic acid, nitrilotriacetic acid,N-2-hydroxyethyliminodiacetic acid, cyclohexanediaminetetraacetic acidand their obvious equivalents. The amine salts r a flowing stream ofsaid emulsion comprises:

1) from about 1 to about 20 percent by weight of a neat soluble oil; (2)polycarboxylic acid chelant spent with metal ions selected from thegroup consisting of calcium, magnesium, aluminum, and heavy metal ions;(3) up to 400 p.p.m., unchelated hardness, expressed as CaCO and (4) thebalance substantially water. If desired, the emulsion may alsocontain 1) an anti-foaming agent and/or (2) a corrosion inhibitor and/or(3) an additional lubricity agent, such additions not exceeding a totalof about 5 percent by weight.

The reused emulsion is further characterized by having a pH in the rangeof about 5 to about 11, but preferably 7 to 10, by the dispersed oilbeing in the form of globules having an average globule diameter in therange of about 1 to 25 microns and substantially no globules having adiameter exceeding about 50 microns, by a preselected globule diameterbeing readily maintainable, by the emulsion being readily filterablethrough a mechanical filter capable of rem( ling solid particles largerthan 10 to 20 microns size but preferably particles larger than 0.5 to 1micron, and by the emulsion being (1) substantially free of solidparticles larger than about 10 to 20 microns but preferably no largerthan 0.5 to 1 micron and (2) free of more than about 0.2 percent of afree oil phase.

If the reused emulsion is a tight emulsion designed for reversing millwork and cutting operation, for example, the reused emulsion is alsofurther characterized by the dispersed base oil being in the form ofglobules having an average globule diameter in the range of about 1 to 2microns and substantially no globules having a diameter exceeding about5 microns.

If the reused emulsion is a loose emulsion designed for use with atandem mill or other operations where more lubricity is required ortolerated, the dispersed oil phase is in the form of globules having anaverage globule diameter in the range of about 2 to 5 microns withsubstantially no globules larger than about microns.

If the reused emulsion is a coarse emulsion designed for cold rollingsteel or aluminum, the dispersed oil phase is often in the form ofglobules having an average globule diameter in the range of about 5 tomicrons with substantially no globules larger than about 50 micronsdiameter.

Each of tight, loose and coarse emulsions are readily filterable whentreated and maintained according to the invention. An important aspectof the invention is the provision for maintenance and control of globulediameters while avoiding emulsion breakage. Even the normally metastableemulsions are maintainable.

Tight emulsions are obtained and maintained upon pumping, mixing orotherwise thoroughly agitating the emulsion and further filtering theemulsion under conditions in which the concentration of unchelatedhardness is below about 100 p.p.m. Coarse emulsions, on the other hand,tend to arise and be maintained under conditions wherein the amount ofunchelated hardness is substantially above 200 parts per million. Thebasic tendency of the emulsion to exhibit fine or coarse globules isdependent upon the materials used to make up the compounded soluble oilconcentrate. It is to be understood that making up and maintaining anemulsion according to the present invention provides an effect that issuperimposed upon the basic nature of the preselected emulsion. The netresult is that the emulsion size moves to a dynamically stable size andis controllably maintainable at such dynamically stable size using thecomposition and method ofthe invention, i.e., upon maintaining theunchelated hardness below about 400 p.p.m. and the pH in the range of 5to 11, a soluble oil emulsionwill reach a dynamically stable globulesize averaging about 1 to microns diameter with substantially noglobules larger than 50 microns diameter.

In carrying out the process of the invention an emulsion is made upgenerally from water and a commercial neat soluble oil of the typedescribed hereinabove. If desired, the emulsion may be made up from theindividual components.

The alkali metal or ammonium or amine salt of polycarboxylic acidchelating agent used according to the invention is added to the wateremployed in making up the emulsion or the chelating agent may be addedto the diluted emulsion in any convenient form, i.e., as a solution,slurry, or dry particulate solid. In any event the chelating agent,usually in the form of a 20 to percent by weight aqueous alkalinesolution, is added in the requisite amount to bring the hardness leveland the pH into the ranges indicated hereinabove. Generally, the wateremployed or the finished emulsion, as the case may be, is analyzed inorder to determine the needed quantity of chelating agent solution.

The completed emulsion is then placed in service in metal shapingoperations. Generally, clean emulsion is circulated from clean storageto the workpiece where it is used. The emulsion flowing off theworkpiece and off the tool or mill is collected as in a sump where someof the particulate matter present settles out. The emulsion may beallowed to settle further in a system with a large inventory ofemulsion, but in general, the emulsion is more or less in constantcirculation. A brief quiet period in a dirty" tank is advantageous inthe collection and removal of tramp oils before subsequent filtration.Thereafter on occasional cycles the emulsion is sampled for analysis,and hardness level and pH are adjusted by the addition of the indicatedrequirements of alkaline solution of chelating agent. The emulsion isthen pumped to clean storage; if desired, the addition of chelatingagent solution may be made to the emulsion in the clean storage vessel.

More preferably the emulsion after settling in dirty storage is filteredbefore sampling, adjusting the hardness and pH levels, and pumping toclean storage. Filtering is conveniently and effectively carried outwith most any mechanical filter, such as one employing a filter paper ormembrane, and especially a filter using a precoat of a siliceousmaterial such as diatomaceous earth. The filter must be capable ofremoving fine particulate matter, preferably all matter coarser than onemicron size. A very effective form of filter for handling large volumesof emulsion rapidly is a tube-type filter using an array of cylindricaltubes formed of wire mesh made of Monel metal having mesh openings inthe range of 0.004 inch to 0.008 inch and coated with a filter aid suchas Celite 545 diatomaceous earth of which about 80 percent of theparticles are finer than about 40 microns. The filter aid forms a filtercake on each tube that retains solids greater than about 1 micron inshortest dimension. The filter tube extends into the emulsion to befiltered providing a very extensive filtering surface Within a compactzone.

The clean emulsion remains in clean storage until use when the cyclecommences again with the pumping of the lubricant-coolant emulsion tothe metal shaping operation. Normally, the retention in clean storage isbrief, being of the order of 5 to 30 minutes unless a very largeinventory of emulsion is used. Lubricantcoolant emulsion so-handled andmaintained remains stable and usable throughout many, many cyclescompleted during the space of from several months to several years andusually during at least 6 months or more of steady use.

The following examples serve to illustrate the invention and not tolimit the scope thereof.

EXAMPLE 1 This example will best be understood with reference to theaccompanying drawing on which there is depicted a schematic flow diagramfor an 18,000 gallon emulsion system. In the diagram there is shown theflow pattern of lubricant-coolant emulsion from the mill rolls of arolling mill, through the conditioning equipment, and back to the rollsin a commercial aluminum rolling mill. In the drawing, the referencenumeral 1 refers generally to an 84inch wide 4-high reversing hot mill.In its operation, 5,000-pound slabs of aluminum ingot (not shown) wererolled from an initial thickness of approximately 14 inches to variousgauges down to a final gauge less than about inch thick, the metal atthe final pass having the form of either sheet or plate. Product fromthis mill must be suitable either as a final product, or as re-rollstock to be further processed before use.

During the rolling operation, a flood lubricant-coolant emulsion, asdescribed above, was applied to the workrolls through a system ofspray-nozzles (not shown). The relative distribution of coolant acrossthe width of the rolls was regulated by adjusting the flow through thevarious nozzles provided. By regulating the degree of cooling of thework rolls from their centers to their edges,

the relative amount of roll clearance from the centers to the edges ofthe rolls is controlled and thereby the flatness of the product ismaintained. The emulsion temperature was in the preferred 120-l30 F.range as it is initially on the mill rolls.

Provision was also made for directing a stream of coolant emulsion ontothe product itself (not shown) as it left the rolls and before it wascoiled or cut in pieces and stacked. Cooling of the metal product atthis stage is often essential to the prevention of surface damage to thefinished product.

In this case, such provision consisted in having the lubricant-coolantemulsion, as it left the work rolls, cascade down over the rolled metalemerging from the mill. The emulsion was carefully removed from therolled metal by jets of air (not shown) that blew it off before thetrnetal moved very far from the mill. Careful removal is important, forresidual coolant on the product may result in staining of its surface.

The coolant athen passed by gravity into a mill pit 2, a 5,000 gallonreservoir beneath the mill, and thence to a 4,000 gallon sump 3. Thesetwo reservoirs serve primarily as collection points for coolant, but avaluable secondary function is that of foam storage. Foam that isgenerated at the mill, particularly in spray-quench operations, needstime to break down, and these reservoirs provide a storage capicity toafford this time. Foam breakdown may be assisted by the addition ofappropriate antifoaming agents to the mill pit contents.

Sump pumps 4 then carried the lubricant-coolant emulsion to a 12,000gallon storage tank 5 which is divided into a 4,000 gallon cleancompartment 6, and an 8,000 gallon dirty compartment 7. From the sump,the emulsion was directed first to dirty compartment 7. From there itwas pumped through a mechanical filter 8 precoated with Celite 545diatomaceous earth, and returned to the clean compartment 6. The filterhas a capacity of 1,500 gallons per trninute, a rate that is faster thanthe normal milldemand rate. Therefore, while the clean and dirtycompartments of the storage tank communicate with each other, normallythe flow not needed in the metal shaping operations was directed fromthe clean compartment 6 to the dirty compartment 7. During temporaryperiods, for example, when the mechanical filter .8 was beingbackwashed, the reverse flow took place, i.e., from the dirtycompartment to the clean compartment. Therefore, a secondary coarsestrainer filter 9 was provided in the system to remove particles largeenough to clog the spray nozzles used at the mill. From the cleancompartment 6 the coolant ordinarily flowed through such secondaryfilter 9 on its way to the mill.

This prevented gross contaminant particles being carried along with thecollant and plugging the spray nozzles (not shown) during such temporaryperiods when the mechanical filter was being by-passed.

The mechanical filter was a tube-type filter, containing about 750 tubesof woven Monel-wire mesh. Each tube was l-inch in diameter and 3 feetlong. The wire diameter was 0.011 inch. The mesh openings have maximumdimensions of 0.006 inch to 0.008 inch while the average openings are0.004 inch x 0.006 inch.

At the start-up of filtration after back-washing the mechanical filter,the filter tubes were precoated with Celite 545 diatomaceous earth, afilter aid of which about percent of the particles are finer than about40 microns. The precoat or filter cake formed on each tube retainedsolids greater than one micron in diameter. The precoat was introducedinto the suction side of the filter pump 10 from a 150 gallon tank 11 inthe form of a suspension containing pounds of filter aid and the balancewater. One-half of the contents of this tank were used to precoat thefilter; thus 50 pounds of filter aid formed the initial cake. Theporosity of the filter was controlled during the useful life of thefilter cake by periodic controlled additions of filter aid, as wellunderstood in the art. These subsequent additions, were made from asuspension known as body feed, which consisted ofabout 50 pounds offilter aid and the balance being 300 gallons of water. Normally, bodyfeed was metered in during approximately three seconds out of eachtrninute at a rate sufficient to provide about 50 pounds of filter aidduring each 24-hour period. In addition to the original 50 poundprecoat,-the filter can handle an additional 200 pounds of body feed.Thus, under normal operating conditions, about five days of filteroperation were attainable between back-washes. When an unusual conditionoccurred, such as excessive leakage of tramp oils into the system, orgreater dirt load from rolling certain alloys; a faster rate of bodyfeed was employed to avoid excessive pressuredrop build-up across thefilter. In this case, the cycle between backwashes was shortened.

The back-wash operation requires about 35 minutes. During back-wash,coolant from the filter vessel was discharged into the 1,500 gallonrecovery storage tank 13. The entire recovery filter cycle takes about 7hours. Filtration of the back-wash to retain used filter aid solids forwaste disposed was accomplished advantageously by making use of acloth-type filter or equivalent (not shown). I

Additions to the emulsion system were made at the following places: (1)replacement of water lost by evaporation and drag-out on the product wasintroduced directly into the dirty compartment 7 (up to 7,000 gallonsper day). De-ionized water was used to minimize introduction ofmagnesium and calcium ions into the system. On occasion, ordinary hardwater was used, i.e., some hardness was deliberately added to minimizefoaming; (2) soluble oil and chelating agent were added at the sump 3;(3) anti-foam agents, if needed, were introduced at the mill pit 2.

Samples for analytical control were removed after the final filteringjust before the lubricant-coolant emulsion was pumped to the mill.

- The composition of the lubricant-coolant emulsion was maintained inthe following manner. The oil phase of the emulsion consisted of 4.5 to6.0 weight percent of a light oil, having a viscosity, at 100 F., of100-200 SUS, emulsified in water with one or more anionic and/ornon-ionic emulsifiers as described above. The emulsion was made up withwater. To the resulting emulsion, there was added an aqueous solution ofan alkaline chelant. The quantity of such alkaline chelating agent usedwas such as to bring the hardness of the aqueous phase of the emulsionwithin a range of 100-200 p.p.m., expressed as CaCO and the pH within arange of 9 to 10, to give the emulsion the desired properties ofstability and lubricity. When the hardnessof the emulsion approached 200p.p.m., more chelating agent was added.

The following analytical control tests were routinely executed todetermine times of addition of additives needed to maintain the desiredproperties of the lubricant-coolant emulsions.

1. Percent soluble oz'L-This test gives the concentration of oil in theemulsion. The concentration is determined by breaking a sample of theemulsion with acid, centrifuging the broken emulsion, and measuring theoil layer. Adjustment of the oil concentration to the desired range isaccomplished by the addition of neat soluble oil or de-ionized water.

2. Percent free il.This is determined by centrifuging a sample of theemulsion for a predetermined time and measuring the oil layer. Generallyone expects only a trace to be visible. Preferably, when the free oillevel reaches from 0.2 to 0.4 percent, chelant salt is added to correctthe problem. When the free oil level reaches a level of 0.6 percent byweight, mill entry problems are encountered because of excess lubricity.

3. Hardness.The concentration of polyva'lent metal ions, such asmagnesium, calcium, and aluminum ions, was maintained in the range of100-200 p.p.m., expressed as calcium carbonate. Additions of chelantsalt were made to prevent build-up above this range. Addition of hardmake-up water was employed to increase hardness on a few occasions whenthe hardness fell below the desired range.

4. Filter time-This test measures the time for one gallon of warmlubricant-coolant emulsion to pass through a double thickness of WhatmanNo. 30 filter paper, 7 centimeters in diameter, under suction.Acceptable range is 5-8 minutes, at a 10 pounds per squareinchdilferential pressure (absolute)- Higher values may indicatemalfunction of the filter leading to excessive dirt build-up, 'or it mayindicate low chelant salt and/ or high tramp oil concentration.

5. pH-Lub'ricant-coolant sample is'diluted to 1 percent and tested witha pH meter. The pH is inherently maintained in the range of 9 to 10 bythe periodic addition of alkaline chelant salt.

EXAMPLE 2 The procedure of Example 1 was followed for a number ofsuccessive mill passes. Both aluminum plate and coil were rolled over aperiod of 7 days. The hardness of the lubricant emulsion graduallyincreased to about 250 p.p.m., calculated as CaCO At this time 15gallons of aqueous 38 percent tetrasodium ethylenediaminetetraaceticacid (Na EDTA) was added to bring the hardness level down to 170 p.p.m.,calculated as CaCO In six more 8-hour shifts of operation, the hardnessbuilt up to 200 p.p.m. of (CaCO At this time, 5 gallons of 38 percent NaEDTA were added and the hardness dropped to 180 p.p.m. (as CaCO whensampled and analyzed 24 hours later. This procedure was repeated againafter four more 8-hour shifts of operation in which the hardness wasadjusted below 200 p.p.m.

Approximately 1 p.p.m. hardness build-up per hour was calculated fromthe Na EDTA additions for the system when rolling aluminum alloyscontaining Mg. In each instance the effect of the Na 'EDTA addition wasto lower and maintain hardness level within the range of 100-200 p.p.m.

During this period, four -gallon drums of soluble oil concentratecontaining emulsifying agent were added. Water losses up to 5,000gallons per 24 hours were made up by adding de-ionized water.

At another time an estimated 200 gallons of hydraulic oil (220 SUSviscosity at F.) entered the system because of a leak.

It was necessary to back-wash the precoated filter six times during aperiod of about 32 hours. The emulsion remained stable and the oilglobules were maintained at an average particle diameter size of about 2microns with'no particles larger than about 5 microns. Lubricatingproperties of the emulsion were completely satisfactory during thisperiod, and filterability permitted continued reuse of the emulsionwhich otherwise would have been discarded. Surface quality of the rolledaluminum product was good to excellent during this time.

EXAMPLE 3 The procedure of Example 1 was followed for a large number ofsuccessive mill passes. Some of each of aluminum plate and coil andmagnesium plate and coil were rolled interchangeably on the same millover a period of 15 months. The hardness of the lubricant emulsiongradually increased periodically to about 250 p.p.m., calculated as CaCOEach time the hardness reachedsuch a level of concentration, about 15gallons of aqueous 38 percent tetrasodium salt ofethylenediaminetetraacetic acid was added to the emulsion to bring thehardness level down to about to 100 p.p.m., expressed as CaCO In eachinstance the hardness level was reduced so as to maintain hardnesswithin the range of about 100-200 p.p.m., expressed as CaCO Occasionallya 55-gallon drum of soluble oil concentrate containing emulsifying agentwas added to the emulsion to make up for base oil taken out by thefilter and especially for accidental spillage or sewerage of theemulsion. Water losses due to evaporation and drag-out amounting to asmuch as 5,000 gallons per 24 hours were made up by adding needed amountsof de-ionized water.

Occasionally a relatively small quantity of hydraulic oil not exceedingabout 200 gallons and having a viscosity at 100 F. of about 220 Sayboltseconds entered the system because of accidental leakage. Such oil wastaken up during pumping and handling of the emulsion, disappeared andwas no longer present as a free coalesced phase.

Throughout the period of use the emulsion was filtered using the filterand precoat described in Example 1. During periods of active use, theemulsion was filtered steadily during transfer from the dirtycompartment 7 to the clean compartment 6. During such times the filterwas back-washed and recoated about every 48 hours.

Throughout the 15 month period the emulsion remained stable and cleanand readily filterable. The oil globules of the emulsion remained instable form with an average globule diameter in the range of 1 to 2microns with no globules larger than about microns. In general, nocoalesced or continuous phase of free oil (in excess of about 0.2percent by weight) appeared except during accidental leakage into thesystem of unusually large quantities'of hydraulic oil. The lubricatingproperties of the emulsion were completely satisfactory during thisperiod and the surface quality of the rolled metal was good to excellentthroughout the entire period.

EXAMPLE 4 Cold rolling of steel is carried out on a 5-stand tandem millin which steel sheet is reduced in thickness from about 0.10 to 0.15inch to about 0.015 to 0.05 inch. During rolling, the steel sheet andthe rolls are lubricated by 1000 gallons per minute of an oil-in-wateremulsion from a recirculating system containing 15,000 gallons ofemulsion. About one galllon of neat oil is applied per 8,000 pounds ofmetal rolled. The base oil used in making up the emulsion is palm oil.The palm oil is emulsified with standard emulsifiers and constitutesabout 3 percent by weight of the emulsion. At the start of using theemulsion, the emulsion pH is adjusted to about 8.5 and the hardnesspresent in the emulsion is adjusted to about 100 p.p.m., expressed asCaCO by the addition of the requisite amount of the trisodium salt ofnitrilotriacetic acid.

During rolling, the emulsion flooding the rolls and cascading over thesheet metal is collected in an underlying sump, pumped to dirty storage,then filtered through a precoated mechanical filter employing asiliceous material for precoating and capable of removing solidparticulate matter larger than 1 micron size. The filtered emulsion iscollected in clean storage and is again promptly reused in the mill.Periodically, the emulsion being pumped to the filter is sampled,analyzed, and the requisite additions of the sodium salt ofnitrilotriacetic acid are made to maintain the pH of the emulsion in therange of 8.5 to 9.5 andthe hardness content of the emulsion in the rangeof 100 to 200 p.p.m., expressed as CaCO Periodically, additions of waterand of neat soluble oil are made to compensate for losses by evaporationand drag-out. Periodic tests show that the oil globule sizes in theemulsion remain stable at an average size of about 15 microns diameterwith substantially no globules larger than 40 microns diameter.

After a period of 19 months, the emulsion remains stable andsubstantially free of continuous free oil phase, the oil globule sizesremain stable at about 15 microns diameter, the sheet steel issatisfactorily reduced in thickness in the rolls and the surface of therolled metal is 12 p smooth and bright and substantially free of surfaceim perfections.

EXAMPLE 5 Cold rolling of brass is carried out on each of a 2-highreversing breakdown mill, a 2-high rundown mill, and a 4-stand tandemfinish mill. In typical operations, continuous cast 26 inch wide fiatbrass bars each weighing about 3,000 pounds are cold rolled from 3.25inch thickness to 0.540 inch gauge flat plate on the breakdown mill.Nine passes and two intermediate anneals are required to accomplish thereduction in thickness. The rolls and workpieces are lubricated by aflow and spray application of 800 gallons per minute of a recirculating,filtered, lubricant-cooled oil-in-water emulsion from a systemcontaining 16,000 gallons of emulsion. The emulsion has a neat solubleoil concentration of about 12 percent by weight, average oil globulediameters of about 1 to 2 microns, a hardness content of to 200 p.p.m.,expressed as CaCO and a pH of about 7.8 to 8.5. Hardness and pH aremaintained by periodic additions of the trisodium salt ofnitrolotriacetic acid to the emulsion. Overhauling (scalping) removesany stain that develops on the rolled plate.

On the rundown mill brass strip is rolled from 0.500 to 0.102 inch thickwithout annealing. On the finish mill, strip is rolled from 0.102 inchthickness to 0.012 inch gauge with intermediate annenals as necessary.The workpieces and the rolls of each mill are cooled and lubricated with650 gallons per minute of a recirculating, filtered lubricant-coolantoil-in-water emulsion from a common system holding 20,000 gallons ofemulsion. The emulsion has a neat soluble oil concentration of about 7percent, an average oil globule diameter in the range of about 5microns, a hardness content maintained in the range of 25 to 75 p.p.m.,expressedas CaCO and a pH of about 7.3 to 7.8. The emulsion is made upfrom the soluble oil Prosol 66, supplied by Socony Mobil Vacuum Company,Prosol 66 soluble oil is low in sulfur compounds and is non-staining ofcopper and copper alloys. Hardness and pH are maintained by periodicadditions to the system of the tetramonium salt ofethylenediaminetetraacetic acid. Routine losses of emulsion are made upadding new emulsion to the system.

After continuous operation of each mill and emulsion system for over 12months, examination of each shows that rolling is carried outsatisfactorily, the rolled brass products exhibit an excellent surfaceappearance, and the reused emulsions are clean and stable and filterablethrough a filter capable of removing solid particulate matter largerthan about 1 micron size.

EXAMPLE 6 In a shop in which precision grinding is carried out, anoil-in-Water emulsion containing 1 percent by weight of a soluble oil issupplied to each of 15 grinders at a rate of 20 gallons per minute andlubricates and cools the workpieces and the grinding wheels. At eachgrinder, the used emulsion flows onto a collecting plate having acentral depression covered by a coarse screen (0.2 inch screen openings)and piping means draining the collecting plate to a common sump.Emulsion collected in the sump is pumped to a filter employing amicrocel membrane which passes particulate no larger than 1 to 2 micronssize. Filtered emulsion collects in a clean storage compartment untilrecirculated to the grinders. The emulsion has an average oil globulediameter in the range of about 1 to 2 microns, a hardness contentmaintained in the range of 100 to 200 p.p.m., expressed as CaCO and a pHof about 8.5 to 9.5. Hardness and pH are maintained by periodicadditions of the disodium salt of N-2-hydroxyethyliminodiacetic acid.Emulsion losses are made up by the addition of fresh soluble oil and tapwater and enough disodium salt of N-Z-hydroxyethyliminodiacetic acid tomaintain the said hardness level. After 13 months of operation theemulsion system is clean and stable, the emulsion globule sizes have notsubstantially changed, and the emulsion remains readily filterable andreusable in the grinding operations. w 1

In a manner similar to each of the foregoing, the sodium, potassium,ammonium, and amine salts of each of ethylenediaminetetraacetic acid,N-hydroxyethylethylenediaminetriacetic acid, N 2hydroxyethyliminodiacetic acid, diethylenetriaminepentaacetic acid,nitrilotriacetic acid and cyclohexanediaminetetraacetic acid are usefulin controlling and maintaining oil-in-water lubricant-coolant emulsionsemployed in metal shaping operations including rolling, working,drawing, cutting, milling, scalping, drilling, machining and grinding ofmagnesium, aluminum, copper and ferrous metal.

The mode of operation of the chelating agents employed in the presentinvention is not clearly understood, but it appears that the polyvalentmetal ion control obtained critically affects the hydrophile-lipophilebalance obtaining in the lubricant-coolant emulsions whereby theemulsions are rendered surprisingly stable and globule diameterssubstantially do not change when the emulsions are managed according tothe invention.

The emulsions managed and reused according to the invention, includingfine filtering are further characterized by surprisingly low ionconcentrations of metals such as aluminum, iron and silicon, the ionconcentrations, respectively, remaining generally below about 1 to 30ppm. Moreover, metal surfaces in continuous or repeated contact with thepresent treated emulsions seem to become passivated toward the emulsionsso that there is little metal ion uptake.

Among the advantages of the invention is the bacterial control achievedwithout the necessity of adding a bactericide. The chelating agentsemployed tie up substantial proportions of metal ions in the emulsionswhich would otherwise react with metal surfaces to provide molecularhydrogen. Molecular hydrogen, which has a powerful catalytic effect onthe growth of anaerobic bacteria, is largely avoided. Moreover, whereinfine filtration is carried out, initial bacterial growth is largelyfiltered out so that colonies are not readily established. Removal ofmetal fines by filtration also removes metal fines which would otherwisecontribute to the electrochemical action which provides the undesiredmolecular hydrogen.

Another advantage of the stable emulsions and the method of theinvention is the avoidance of the problems associated with (1) cleaningup a system after an emulsion breaks, and (2) starting up a system witha completely new emulsion or after a major addition to a used emulsion.New emulsions need to be used up to 2 weeks before they exhibit reallygood filterability. Even major additions, e.g., at least one-fourth ofsystem capacity, necessitate shorter filter cycles for some days.

The method and composition of the invention having been thus fullydescribed, various modifications thereof will at once be apparent tothose skilled in the art and the scope of the invention is to beconsidered limited only by the breadth of the claims hereafter appended.

I claim:

1. In a method of cooling and lubricating a metal during the shapingthereof wherein the work piece and the tool are contacted with a flowinglubricant-coolant oil-in-water emulsion and said emulsion is recycledand reused steadily, in said shaping, over a period of at least severalmonths, the steps which comprise:

adjusting and maintaining (1) the hardness level of the aqueous phase ofthe emulsion below about 400 p.p.m., expressed as CaCO and (2) the pHvalue of the emulsion within the range of about 5 to 11 by periodicadditions to the emulsion of the requisite amounts of a chelant selectedfrom the group consisting of alkali metal salts, ammonium salts andamine salts of a polycarboxylic acid chelating agent whereby theemulsion is-stablized and is further characterized by readyfilterabilityj and passing from about one-third tosubstantially all ofsaid emulsion, afteruse and prior'to reuse, throughamechanical filter;said metal being selected from the group consisting of aluminum, copperand ferrous metal.

2. The method as in claim 1 wherein the hardness is maintained in therange of about 25 to 400 p.p.m., expressed as CaCO 3. The method as inclaim 1 wherein the hardness is maintained in the range of about to 200p.p.m., expressed as CaCO 4. The method as in claim 1 wherein the pH ismaintained in the range of about 7 to 10.

5. The method as in claim 1 which includes the further steps ofperiodically sampling and. analyzing the emulsion for hardness and pH,and adding chelant in the requisite amount to maintain each of thehardness level of the aqueous phase and the pH value within the saidranges.

6. The method as in claim 1 in which mechanical filtration is carriedout to remove from the emulsion particles larger than a preselected sizein the range of about 0.5 to 10 microns.

7. The method as in claim 1 wherein the chelant employed is a salt of analkylene amino polyacetic acid.

8. The method as in claim 1 wherein the shaping method is rolling andthe emulsion comprises (1) from about 2 to about 15 percent by weight ofneat soluble oil, (2) spent chelant, the chelant being combined withpolyvalent metal ions, (3) from about 25 to 400 p.p.m. of unchelatedhardness, expressed as CaCO and (4) the balance substantially water, andthe further steps which comprise:

(a) contacting the rolls and the metal work piece with said emulsion asthe work piece enters the rolls of the mill;

(b) passing said work piece between said rolls thereby to reduce thethickness of said work piece;

(c) collecting said emulsion after use on the work piece and the rolls;

(d) analyzing said emulsion for hardness;

(e) adding an alkali metal salt, ammonium salt, or amine salt of apolycarboxylic acid chelating agent to the emulsion in the requisiteamount to adjust the hardness content of the aqueous phase of theemulsion to 25 to 400 p.p.m., expressed as CaCO and the pH' to a valuein the range ofabout 7 to 10;

(f) passing at: least of said emulsion after use through a filterthereby to remove solid particles larger than a predetermined size inthe range of about 0.5 to 10 microns;

(g) and recycling said filtered emulsion from the filter to the saidrolls.

References Cited UNITED STATES PATENTS Re. 23,905 12/1954 Bersworth260-518 2,631,978 3/1953 Bersworth 252-33.6 2,663,704 12/1953 Yehling260217 2,770,597 11/1956 Jezl 252-495 XR 2,780,598 2/ 1957 Cafcas252-34'.7 XR 2,794,000 5/1957 Ruedrich 252-495 XR 2,802,788 8/1957Flaxman 252-l05 2,959,547 11/1960 Brillhart 25233.6 2,432,784 12/1947Miller 252-49.3 3,301,783 1/ 1967 Dickson et a1. 252-49.S XR 2,264,10311/ 1941 Tucker 210-23 (Other references on following page) 16 1 7 QTHER FE gENcEs if l igjry qfi limi i i nsj, s n Edition, 954, Tin; BlapkLubricating Engineering I, Octobverv1951, pp. 223-227. t 1119, P b- C nPP ,3 fi 2-2 Lubrication Engineering II, July 1959, pp. 85-99.Metak,Industry,;April 1958, pp. 27 1-273,'Fish1ock. i DANIEL E,- A m WChemistry; of theuMetal Chelate Compounds, Prentice- 5 Hall Inc., Pub.1953, Marten et 211., pp. 4s7 49s and w- N v

